More planets than stars in our galaxy

How common are Earth-sized planets? A study dealing with this question was officially published on January 11, and independently from that, a graphic from NASA appeared the day after, illustrating another extrapolation from recent data taken by NASA's orbiting Kepler spacecraft. According to the latter estimate, which is based on planets (including unconfirmed candidates) discovered in close orbits around their stars, computer models are indicating that at least one in ten stars are orbited by an Earth-sized planet, making our Milky Way Galaxy the home to over ten billion Earths. And there would be even more super-earth-sized planets with up to twice the mass of our homeworld, as well as Neptune sized worlds, as can be seen on the graphic.

But the numbers could be even higher according to the study "One or more bound planets per Milky Way star from microlensing observations", published in Nature this week. The researchers is to extrapolate the number of potential planets by statistical analysis of planets found with the microlensing method, which can discover planets that are relatively far away from their stars, by the very slight gravitational 'wobble' of a star caused by the planets orbiting it. The result is that around 62 percent of all the 100 billion stars in our Milky Way have super-earth class planets, 52 percent host cool Neptune-like planets, and still 17 percent could be circled by Jupiter class giants.